Production flame cutting machines, including oxy-fuel or plasma systems, need means to support the plate stock being cut. To limit fumes and to cool the plate during the cutting operation, the plate is often supported at or just beneath the surface of a pool of water. Such water table systems facilitate operator access to the plate by lowering the water level while the operator loads or unloads the table.
An early use for the water table was for oxy-fuel cutting (e.g., oxygen-acetylene cutting) steel plate. The steel plate was supported in the water table by placing bars beneath the plate. See for example U.S. Pat. No. 4,121,808 issued Oct. 24, 1978 to Jerry F. Cardea. To minimize damage to the bars from the heat of the cutting torch, the support bars were constructed from material having high thermal conductivity, such as copper or aluminum. More recently, electric plasma torches forced a change to less expensive steel support bars because the much higher temperatures which plasma torches generate can easily melt aluminum, copper, or steel supports.
Although steel bars reduce support replacement cost, they have other inherent problems. When the cutting path crosses the steel support bars, the plasma torch cuts the bars as it cuts through the steel plate. In addition, the plasma cut generates molten metal slag which accumulates on the support bars eventually making the support surface uneven. An operator must frequently remove this slag to maintain cut quality. Eventually, the bars become unusable and must be replaced. The operator must also separate plate sections from support bars which slag welds together during the cutting process. Further, cut quality can be adversely affected when the plasma torch cuts along a substantial path directly above a support bar. Parts shorter than twice the distance between adjacent support bars may tip after being cut and can damage the cutting torch if they collide as the torch cuts adjacent parts. Steel support bars can adversely affect cut quality, can damage equipment, and require frequent operator intervention to remove slag which accumulates on the bars, to separate parts which become welded to the support bars, and to replace unusable support bars.
To avoid some of the problems inherent with steel support bars, discrete supports have been placed beneath the steel plate for support. Examples of these discrete supports include a plurality of metal cups, cones, or short lengths of tube. See for example U.S. Pat. No. 4,524,955 issued Jun. 25, 1985 to Peter W. Boardman. Copper, aluminum, or steel supports of this type are easily melted by plasma torches. In addition, steel discrete supports share many of the problems inherent with steel bars; an operator must intervene to remove slag which accumulates on the supports, to separate parts which become welded to the supports, and to replace damaged supports.
An inherent problem associated with these discrete supports is the need to accurately place them beneath the workpiece. The operator must position the discrete supports so they can avoid the torch cut path while continuously supporting the workpiece and the scrap plate which the torch cuts away. Further, the discrete support positions must change when the burn table is to be used to cut a different part from plate stock.
The present invention is directed to overcoming one or more of the problems set forth above.